Water disintegrable lead shot



United States Patent 3,463,637 WATER DISINTEGRABLE LEAD SHOT George S.Foerster, Midland, Mich., assignor to The Dow Chemical Company, Midland,Mich., a corporation of Delaware No Drawing. Filed Aug. 26, 1966, Ser.No. 575,232

Int. Cl. C22c 11/02 US. Cl. 75--167 6 Claims ABSTRACT OF THE DISCLOSUREA lead-base alloy contains, by weight, from 2 to 6 per- 3' The inventionrelates to a novel lead alloy and more particularly relates to a leadalloy suitable for the prep aration of bird shot.

The problem of poisoning ducks and other bottomfeeding water fowl withlead shot has been recognized for a long time and has become moreserious because the increasing numberof nimrods has increased the concentration of residual lead shot in popular hunting areas.

The problem arises wherein-shot does not find its target and falls intorelatively shallow water where it is mistaken for gravel by water fowland ingested.

It has been proposed heretofore to employ lead alloy containingmagnesium. However, lead shot made from lead alloy containing magnesiumas the sole alloying additament'and shotted ina shooting tower has'notdisintegrate'd'rapidly, if at all; on immersion in water, but ha tendedto merely crack slightly without opening.

--It --is therefore a principal object of the present inven-' tion toprovide an improved lead alloy for the preparation of lead shot whichwill crack open or disintegrate rapidly during immersion inwater atambient room temperature.

Another object of the invention is to provide a waterdi'sinte'gr'ablelead. alloy from which there can be prepared lead shot having sufficientdensity for accurate shooting. These and, other objects and advantagesof the present invention 'willbe more clearly understood upon becomingfamiliar with the following description and the illustrative examples.--

It is now been found that upon preparing a lead-base alloy comprisingfrom about 2 to about 6 percent by Weight of magnesium, up to about 6percent by weight of mercury, up to about 3 percent rare earth metal andthe balance substantially lead and at least one of the alloyingcomponents of mercury and rare earth metal being present in the alloy ata concentration of at least 0.2 percent by weight and the said alloybeing prepared as substantially spherical lead shot, the so-providedshot is characterized by ready cracking open or disintegration uponimmersion in water at ambient room temperature for about 24 hours.Preferably the alloy contains from 2.5 to 3.5 percent by weight ofmagnesium and from 0.5 to 1.5 percent by weight of mercury. In anotherpreferred embodiment, the alloy contains from 0.5 to 2 percent by weightof rare earth metal, desirably in combination with both of magnesium andmercury. Even though the mag nesium content of the present alloy isrelatively high, the alloy has a density such that good reproduciblecarry is 3,463,637 Patented Aug. 26, 1969 realized and a high order ofaccuracy is attainable on shooting shot made of the alloy.

The lead alloy is readily prepared in a conventional manner by heatinglead and the alloying constituents together to a temperature of about650 to 700 F. or higher. Generally, higher temperatures are employed inconnection with the alloy containing rare earth metal. Meltingtemperatures of about 1000 F. are used in order to dissolve rare earthmetal in the molten lead. Melt temperatures above about 700 F. aretypically used to keep the rare earth metal dissolved in the melt. Rareearth metal is more easily added after the addition of magnesium whichincreases the solubility of the rare earth metal in the molten lead.Rare earth metal can best be added to the lead as a master alloy ofmagnesiumrare earth metal. Lanthanum, being about the most soluble ofthe rare earth metals commercially available, is a preferred rare earthmetal.

It is preferred to add mercury to the alloy after all other alloyingadditions and at as low a temperature as possible, e.g., about 500 to600 F. if rare earth metal is not present in the alloy, to avoidvolatilization of the mercury. Lower temperatures also favor theretention of the megnesium content of the melt. The lead used in makingthe alloy is preferably substantially free of antimony, bismuth, tin, orother elements which tends to form solid-insoluble phases orintermetallic compounds with magnesium, as well understood in the art.The lead can be made sufficiently free of such elements, if necessary,by adding magnesium to the molten lead and skimming off the insolublephases. The Pb-Mg alloy is then analyzed and additional magnesium isadded, if needed, to make the intended composition.

Generally the alloy is allowed to settle briefly, any insolubles presentare skimmed off, and the molten metal is then cast into molds or shottedin a shot tower while the melt is at a temperature in the range of 500to 700 F., or higher if necessary to retain the rare earth metalcontent. Where molds are used, the molds are generally brought to atemperature in the range of about 200 to 450 F. just prior to castingthe metal.

If desired, the present alloy may be cast as a billet. The billet isthen reduced to shot mechanically, for example, by extruding the metalinto wire or rod which is cut into short pieces and worked intosubstantially spherical form.

. agglomerating methods.

For the purposes of this description and the appended claims, theexpressions water disintegrable shot and shot subject to readydisintegration are understood to refer to shot which does more thanexhibit surface cracks or split into two or three major pieces, butcracks into a number of pieces or becomes-friable or both whileotherwise retaining integrity of structure, or further, fal-lscompletely apart without mechanical agitation.

The following examples serve to illustrate the invention and are not tobe considered as limiting the scope thereof.

In a series of runs according to the invention, lead melts containingvarious amounts of magnesium with or without mercury and/ or rare earthmetal were prepared by melting the metals together in a conventionalmanner, the magnesium being added first in each case. The rare earthmetal employed was misch metal, a commercially available mixture of rareearth metals. Samples of each alloy while at a temperature of about 600to 700 F. were cast into inch diameter pellets in molds maintained at250 and 450F., respectively. Two pellets of each alloy, respectively,from each mold were placed in respective bottles containing tap waterand observed periodically until bubbling, i.e., gas generation, stopped.Generally, bubbling did not continue more than two days. Each pellet wasthen examined visually and its final condition rated. The nominalcompositions employed and the ratings on visual examination aresummarized in the following table. The actual compositions are generallysomewhat lower than nominal values. In general, reactivity increasedwith increasing proportion of mercury in the lead alloy. The alloyscontaining percent by Weight of mercury stopped reacting in less than 22hours.

In additional runs made by way of comparison, lead melts were preparedcontaining magnesium but no mercury or rare earth metal, The comparisonalloys were similarly cast into pellets and immersed in water. Thecompositions of the comparison alloys and the condition of the pelletson visual examination are also listed in the table.

The lead alloy and lead shot of the invention having been thus fullydisclosed, various modifications thereof will at once be apparent tothose skilled in the art and the scope of the invention is to beconsidered limited only by the breadth of the claims hereafter appended.

IClaim:

1. A lead-base alloy consisting essentially of from about 2 to about 6percent by weight of magnesium, from about 0.2 to about 3 percent byweight of rare earth metal, up to about 6 percent by weight of mercury,and the balance lead.

2. The alloy as in claim 1 which contains'from about 0.2 to about 6percent by weight of mercury.

3. The alloy as in claim lwwh ich contains from about 2.5 to 3.5 percentby weight of magnesium.

4. The alloy as in claim 1 which contains from about 0.5 to 1.5 percentby weight of mercury. I

5. The alloy as in claim 1 which contains from about 0.5 to 2 percent byweight of rare earth metal.

6.'Substantially spherical lead shot formed from lead- TABLE I.FINALCONDITION OF PELLETS TESTED Composition, by weight Percent PercentPercent Run No. Mg Hg MM Mold temp., 450 F. Mold temp., 250 F.

Comparison 1 2. 5 0 Cracked, 2 pieces broke ofL Few small cracks.

4 0 Little disintegration at surfa Crac e Comparison 2- 1 2. 5 1 Brokeinto few large pieces. Broke into many pieces. 2. 5 5 Cracked wide openCracked open, 1 piece broke ofi.

4 1 Approx. disintegrated, rest friable. Dlsintegrated. 4 5Disintegrated Broke into large pieces. 3 1 Cracked into pieces. Crackedinto pieces. 3. 5 1 Cracked Wide open Cracked wide open.

4 5 Cracked wide open, some disinte- Cracked wide open, somedisintegration. gration. i ..i. Cracgred slightly open Cracged slightlyopen.

o-- o. 4 2 Considerable flaking oti surface Considerable flaking onsurface. 3.5 1 1 Broke apart, some disintegration Broke apart, somedisintegration.

4 1 Disintegrated Disintegrated.

Balance lead.

MM=misch metal, a commercially available mixture of rare earth metals.

In two additional runs which illustrate the invention, lead melts weremade up in the same manner as described in the foregoing runs and castinto 3/16 inch diameter pellets in a similar manner using a mold whichwas at a temperature of about 400F. at the time of casting. Severalpellets of each alloy, respectively, were placed in respective bottlescontaining tap water and observations were made periodically untilbubbling stopped in about 24 hours. Pellets of each alloy were alsoanalyzed to determine actual composition. The nominal and actualcompositions of each alloy and the results of the water immersion teston final visual examination of the pellets are listed in Table II.

Actual composition values are shown in parenthesis.

base alloy consisting essentially of from about 2 to about- ReferencesCited UNITED STATES PATENTS 862,778 8/1907 Williams -166 1,360,34711/1920 Worrall 75-167 1,428,041 9/1922 Kroll 75166 2,167,828 8/1939Dowdell et al 75167 X CHARLES N. IiOVELL, Primary Examiner U.S. Cl. X.R.29-192; 75-.5

